After receiving the Covid-19 vaccine, your body will be prompted to mount an immune response. This might result in some reactions that are typical of other vaccinations as well. Here are some commonly reported side effects of the the Pfizer-BioNTech and Moderna mRNA vaccines, which are approved for use in Singapore.

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In general, the side effects of both vaccines are quite similar and can be summarised as such:

Common side effect	What to do
Pain, redness, swelling at injection site	Take 1 to 2 tablets of Paracetamol every 6 hours as needed. Dress lightly; drink plenty of fluids; apply a wet washcloth over swelling.
Fever, chills
Muscle aches and joint pain
Headache
Tiredness	Rest
Lymph node swelling at neck or arms	Rest; this will resolve by itself in a week

Source: Ministry of Health, Singapore and Centers for Disease Control and Prevention (CDC), United States

Side effects in detail

For those who wish to delve into the details of reported side effects of the Pfizer-BioNTech Covid-19 vaccine, the assessment by the Health Sciences Authority (HSA) says: “…some people may experience side effects such as pain, redness, swelling at the injection site,  fatigue, headache, muscle ache, fever, chills, vomiting, diarrhoea and joint pain after vaccination.”

Side effects of the Moderna Covid-19 vaccine as stated in the HSA’s assessment: “Some common side effects that vaccine recipients may experience include pain, swelling at the injection site, fatigue, headache, muscle ache, fever, chills, vomiting, and joint pain after vaccination. Of these symptoms, some (such as fatigue, headache and muscle/joint ache) may be more severe in a small number of persons.”

Manage side effects at home

These side effects can be managed at home without having to see a doctor. You should contact your doctor or healthcare provider:

• If the redness or tenderness where you got the shot increases after 24 hours
• If your side effects are worrying you or do not seem to be going away after a few days

The Centers for Disease Control and Prevention (CDC) in the United States does not recommend that one takes over-the-counter medicine (such as ibuprofen, acetaminophen, aspirin, or antihistamines) before the jab to prevent side effects.

With the Pfizer and Moderna Covid-19 vaccines, you will need two shots in order to receive maximum protection. You should get the second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get it.

Recognising allergic reactions

Serious adverse reactions could be indicative of an allergic reaction. These could be:

• A bad rash all over the body
• Hives
• Shortness of breath
• Dizziness
• Angioedema (swelling of eyelids, lips and face)

Please seek medical attention immediately if you develop such reactions after your first shot. Call 995 or head to the nearest Accident and Emergency department. Your healthcare provider will report the adverse event to HSA. 

Persons with an allergic reaction to the first dose are advised not to take the second dose and should cancel the appointment for it. The Ministry of Health will track this group of individuals and update when there are suitable vaccines available.

HSA is monitoring these rare but severe adverse effects with interest:

• Anaphylaxis, a rare and potentially life-threatening allergic reaction where the patient’s airways narrow
• Bell’s Palsy, also known as peripheral facial nerve palsy, a condition that causes temporary weakness or paralysis of the facial muscles
• Limb numbness and change in vision

Based on data collected since the vaccinations were rolled out on Dec 30, 2020 to Apr 18, 2021, HSA received 2,796 reports on suspected adverse effects. This made up 0.13 per cent of the more than 2.2 million administered doses during this three-month period. 

The local incidence rate of anaphylaxis is 1.4 per 100,000 doses administered, which is well within the reported incidence rates of about 0.5 to 2 in other countries.

What to expect

It is important to differentiate between allergic reactions and side effects. Pain, discomfort and normal side effects are expected.

You may experience more intense side effects after your second shot. These side effects are normal signs that your body is building protection and should go away within a few days. Most side effects will resolve within three days. Though uncommon, lymphadenopathy (lymph node swelling) can be vaccine-related, and takes around 7 to 10 days to resolve.

Your body will take time to build immunity after the vaccination. You will only be considered fully vaccinated two weeks after your second shot of the Pfizer-BioNTech or Moderna Covid-19 vaccine. 

While the side effects of vaccination may inconvenience you, these are just temporary. Getting vaccinated has more far-reaching benefits than disadvantages, such as protecting yourself and, in particular, vulnerable people in the community who are at increased risk for severe illness from Covid-19.

This article has been verified medically by Dr Leong Hoe Nam, infectious diseases specialist at Rophi Clinic, Mount Elizabeth Novena Specialist Centre (Singapore).